Electrochemical battery employing bonded lead dioxide electrode and fluoroboric acid electrolyte

ABSTRACT

A lead dioxide electrode structure for an electrochemical battery employing fluoroboric acid as an electrolyte is formed from lead dioxide particles, a bonding material and preferably a synthetic fibrous material. The bonding and fibrous materials are mixed with the lead dioxide particles to form a compact and homogeneous electrode structure. The bonding and fibrous materials are partially resistant to the fluoroboric acid and are compatible with each other. The battery formed from the electrode structure is operable at temperatures as low as minus 60* centigrade and at temperatures as high as plus 100* centigrade and can be custom made to provide a variety of steady or pulsed current discharges.

United States Patent [191 Weissman et al.

[451 Nov. 6, 1973 1 ELECTROCHEMICAL BATTERY EMPLOYING BONDED LEAD DIOXIDE ELECTRODE AND FLUOROBORIC ACID ELECTROLY TE Inventors: Eugene Yehuda Weissman,

Glendale; Guy Douglas McDonald, Shorewood; Conrad Eugene Weinlein, Milwaukee, all of Wis.

Assignee: Globe-Union 1nc., Milwaukee, Wis.

Filed: ,Jan. 24, 1972 Appl. No.: 220,241

US. Cl. 136/26, 136/118 Int. Cl. [101m 39/00, HOlm 17/00 Field of Search 136/26-27, 6, 64,

References Cited UNITED STATES PATENTS 10/1933 Johnstone....' 136/26 5/1954 Weil et al. 136/26 10/1962 Urry 136/24 12/1962 Solomon et al 136/30 7/1965 Wells 136/6 PL ASTIC COATED P110 POWDER.

DYNEL FIBERS 3,227,583 1/1966 Carlisle 136/6 3,318,794 5/1967 Kiyohara et al. 204/290 3,488,218 l/1970 Metzler et al 117/201 3,496,020 2/1970 Jackson et al. 136/26 3,629,007 12/1971 Kilduff 136/27 3,173,809 3/1965 Hall 136/19 Primary ExaminerAnthony Skapars Attorney-John Phillip Ryan et al.

[57] ABSTRACT A lead dioxide electrode structure for an electrochemical battery employing fluoroboric acid as an electrolyte is formed from lead dioxide particles, a bonding material and preferably a synthetic fibrous material. The bonding and fibrous materials are mixed with the lead dioxide particles to form a compact and homogeneous electrode structure. The bonding and fibrous materials are partially resistant to the fluoroboric acid and are compatible with each other. The battery formed from the electrode structure is operable at temperatures as low as minus 60 centigrade and at temperatures as high as plus 100 centigrade and can be custom made to provide a variety of steady or pulsed current discharges.

11 Claims, 6 Drawing Figures NICKEL TAB 5 l fl l z MPLFETED l CO I I l H ELE C I' RODE I I l] SHEET LEAD COUNTER ELECTRODES PAIENTEDuov 6 ma 3.770.507

SHEET 1 or 2 I PLASTIC COATED PbC) POWDER DYNEL FIBERS NICKEL TAB COMPLETED l ELEcT RODE SHEET LEAD COUNTER ELECTRODES J v FIG. I

L0vv RATE/HIGH TEMPERATURE DISCHARGE OF THE FLUOROBORIC ACID CELL LOO-- CELL- CURRENT DENSITYflrm/m 1 POTENTIAL, TEMPERATURE, soc

VOLTS 0.00 a I HOURS P/IIIIIIEIIIIII 6 I973 3.770.507

SHEET 8 BF 2 2.00 I I I I I I |.5o FIGlI CELL I.25- POTENTIAL, voI Ts I.oo--

CURRENT DENsITY,

lOmd/cm 0.50 i I I I I I o 10 I5 5o DISCHARGE TIME, MINUTES I I FIGI l I l COMPLETE DISCHARGE 2o- COULOMBIC" EFFICIENCY I 1o ABOVE ONE VOLT TEMPERATURE, 23C 0 I i i I I00 150 200 GEOMETRIC CURRENT DENsITY,ImcI/m 2 I I I l' I 30-- 2o-- COULOMBIC EFFICIENCY CURRENT DENSITY, IOmd/CM VOLTAGE CUT-oFF, 1vol+ -40 '20 O 20 4O 6O o TEMPERATURE, C

I ELECTROCHEMICAL BATTERY EMPLOYING BONDED LEAD DIOXIDE ELECTRODE AND FLUOROBORIC ACID ELECTROLYTE BACKGROUND OF THE INVENTION This invention relates to a primary battery of the reserve type and more particularly, to a primary battery for use with fluoroboric acid as an electrolyte employing particular types of bonding materials andsynthetic fibers to form an electrode structure.

Electrodes formed from bonding lead dioxide with resinous materials are described in U.S. Pat. No. 3,318,794. The electrodes therein described are stated to be useful as anodes for oxidation electrolysis. Reserve battery electrodes using bonded active materials are reviewed in an article published by T. J. Kilduff and E. F. Horsey in the 24th'Power Sources Symposium 1970 proceedings of May 19 through May 21 P30-35. The reserve battery therein described is proposed for use with fluoroboric acid as an electrolyte and the electrode therein described consists of a steel shim substrate coated with a conductive material which in turn is overlaid with a coating of lead dioxide in a resinous matrix. The prior art nowhere describes a reserve battery employing fluoroboric acid as an electrolyte which will operate at both low and, particularly, high temperatures for long periods of time. Neither is there available a reserve battery which utilizes a fluoroboric acid electrolyte which can be formed without a metallic substrate for the cathode.

It is-an object of the present invention to provide a novel primary reserve battery which is operable for substantial periods of time over a wide temperature range. It is another object of this invention to provide a reserve battery employing fluoroboric acid as an electrolyte in which the metallic substrate for the cathode can be eliminated/It is still another object of the present invention to provide an electrode structure for use in contact with fluoroboric acid which is readily adaptable for use in both high rate and low rate type batteries. It is still another object of this invention to provide a novel reserve type battery which has wide temperature ranging capabilities and can be produced at low cost.

SUMMARYOF THE INVENTION The I foregoing objects are accomplished and the shortcomings of the prior art are overcome by the present electrochemical battery electrode which is comprised of lead dioxide uniformly mixed with a bonding material and preferably a synthetic fibrous material. Both the bonding and fibrous materials are partially or totally inert to fluoroboric acid yet are compatible with each other and with the lead dioxide in that good cohesion' is afforded yet access to the lead dioxide is afforded the fluoroboric acid electrolyte through selective consumption of the lead dioxide active material. The combined bonding and fibrous materials form a matrix for the lead dioxide which in itself is selfsustaining or can be composited with a metallic or nonmetallic grid or substrate.

BRIEF DESCRIPTION OF DRAWINGS A better understanding of the present battery electrode will be accomplished by reference to the drawing wherein:

battery of this invention at minus 60C and plus 23C.

FIG. V shows the effect of discharge rate on the coulombic efficiency (which is available capacity) of the lead dioxide electrode of this invention.

FIG. Vl illustrates the effect of temperature on the coulombic efficiency of a battery fabricated with the novel electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the following Examples, certain bonding and fibrous materials will be referred to by their trademarks or by abbreviation. All of the materials are readily available on the commercial market and a brief explanation of them is given:

NAME PRODUCT SOURCE Geon 222, 42] Vinyl chloride/ B.F. Goodrich Co. and 427 Vinyl acetate copolymer Dynel' Vinyl chloride] Union Carbide Corp.

' acrylonitrile copolymer Dow Corning 107 Silicone grease Dow Corning Low molecular wt. Union Carbide Corp.

ethylene oxide Ps xm r High molecular wt. ethylene oxide Carbowax 20M 8:. 6,000

Polyox WS R-3 01 Union Carbide Corp.

polymer QP-4400 & 52,000 Hydruxyethyl Union Carbide Corp.

cellulose VMCH Vinyl chloride] Union Carbide Corp.

vinylacetate HM copolymer PA-4459 Thermoplastic Minn. Mining & Mfg. Co. V V adhesive T-30 Tetra fluoroethylene Dupont dispersion The.invention is disclosed in further detail by means of the following examples which are set forth for the purpose of illustrating the invention, but, in no way are to be considered as limiting the invention to the precise amounts, ingredients, or conditions indicated.

EXAMPLE I A 10 percent by weight solution of Geon 421 in methylethylketone is prepared by employing 6.0 grams of Geon 421 in 54.0 grams of methylethylketone by suitable stirring and mixing. Lead dioxide of the Fisher technical grade type and in an amount of 194 grams is dried at C. under reduced pressure (e.g. 150 mm Hg absolute). The dried lead dioxide and the Geon solution are hand-mixed for 30 minutes and the methylethylketone is subsequently removed under high vacuum (e.g. 10 microns absolute pressure) and with a cold trap at room temperature. Any large pieces of material are broken up every hour for 3 hours and the resulting material evacuated overnight at 60C. Subsequently, the resulting mixture is reduced to a fine powder by cooling to liquid nitrogen temperature and blending for 10 seconds. The cooled material is sifted through a mesh screen using a sonic sifter with an amplitude of five and a pulse rate of six over a time of 5 minutes. The sifted material is then heated to 100C with microns pressure for 2 hours and subsequently stored in a dessicator. This material is illustrated in the drawing as 11.

EXAMPLE II A current collector tab 12 is next formed by cutting expanded nickel grid to form a rectangular tab of 0.25 inches by 1 inch. The nickel tab is cleaned by dipping in tricholoroethylene followed by a methanol rinse.

EXAMPLE III An electrode structure 23 is fabricated by mixing 0.20 grams of Dynel fibres 14 with 19.8 grams of the coated lead dioxide mixture 11 formed in Example I to form a 1 weight percent Dynel mixture. A single action die is coated with Dow Corning 107 compound release agent and the die is loaded by adding one gram of the lead dioxide-Geon mix to the die and leveled. The nickel tab 12 described in Example II is inserted and 4 grams of the lead dioxide mixture containing the fibres is added to the die and is leveled also. The die plunger is next inserted in a careful manner and the die placed in a Carver type press, preheated to 120C. and allowed to warm under 2,000 lb. load until the die reaches 120C. A press load of 20,000 lbs. is applied for six minutes at 120C. and the die subsequently transferred to cold press and allowed to cool under minimum clamping pressure of approximately 600 lbs. The grid structure 23 is removed from the die and the tab 12 is coated with a methylethylketone solution of l0w% Geon.

As shown in FIG. II, the formed electrode structure 23 is assembled into a battery unit by positioning it between two lead electrodes 21. Shorting of the battery is prevented by placing separators 22 between the plates. A battery is fabricated in the normal manner by interconnecting several of the grid structures, electrodes 21 and separators 22 in a battery casing (not shown) with the fluoroboric acid electrolyte.

If it is desired to utilize a well known nickel grid for a substrate and a current collector, this can be effected in accordance with the following Examples.

EXAMPLE IV A Geon coated lead dioxide, Dynel matrix mixture is prepared as indicated in EXAMPLES, I, II, and III.

EXAMPLE V A metal grid substrate is formed by cutting expanded metal nickel grid to fit a die cavity 1 inch by 1% inches with a 1% inch by /4 width tab.

The nickel grid is cleaned by dipping sequentially in the following solutions: trichloroethylene, 50 percent nitric acid, distilled water, trichloroethylene, methanol.

The cleaned grid is passivated by cathodizing in a 3 percent nitric acid solution at room temperature and at 129 ma/in for 10 seconds using nickel coated electrodes. Anodizing is effected in the same indicated solution for passivating using 516 ma/in for 3 seconds followed by a 30 second treatment at 129 ma/in The anodized material is rinsed in distilled water.

Beta lead dioxide is plated on the passive nickel grid by anodizing the nickel grid at 129 ma/in for 4 minutes with leadcoated electrodes in a plating solution composed of 240 grams of L-G2 lead nitrate dissolved in distilled water to make a 500 ml solution. L-G2 lead nitrate is available from Fisher Scientific Company. The plated electrodes are rinsed in distilled water using a standard air drier.

EXAMPLE VI An electrode structure is formed using the lead dioxide, resinous bonding and fibrous materials prepared in Examples IV & V by loading a die of the single action type which is previously coated with Dow Corning 107 release agent with 0.5 grams of the lead dioxide, resinous and fibrous materials mixture and the material leveled in the die. The lead dioxide plated nickel grid is inserted in the die and 0.5 grams of the mixture is added and leveled. The plunger is inserted carefully and the die placed in a Carver type press and preheated to C. and allowed to warm up under a 2,000 pound load until temperature of die reaches 120C. which usually takes approximately ten minutes. The press is operated at a 16,000 pound load for 20 minutes at 120C. The die is subsequently transferred to cold press and allowed to cool under minimum clamping pressure of 600 pounds. The electrode is then removed from the die and the tab coated with a 10 percent Geon solution.

As indicated, earlier, a battery can be fabricated from the electrode structure prepared in Examples IV, V & VI by following the previous procedures for battery fabrication shown in FIG. II.

In the preceding Examples, Geon 421 is listed as the preferred bonding material. As shown in Table I it has been found that other resins and some waxes such as carbowax can be employed. The important aspect of the bonding material being that it must have good cohesion with the lead dioxide as well as with the fibrous materials and possibly chemically react in a favorable way with the fibrous material. Further, it and the fibrous material must be combined with the lead dioxide active material so as to permit a sustained exposure of the lead dioxide to the electrochemically reacting fluoroboric acid. The unexpected performance of the bonding materials is evidenced by the fact that several of them which were tried either failed completely or certain percentage mixtures of them could not be utilized. For example, PA-4,459 in a 2w% solution, Polyox WSR-30l in a 3w% solution could not be utilized to advantage, nor could WSR-301 QP4,400 WSR-30l QP52,000 or carboxymethyl cellulose. Further polyvinyl alcohol, T-30 (Teflon dispersion) and Carbowax 20M below 5w% could not be utilized to advantage.

Dynel is an example of a preferred material for forming the fibrous matrix. However, carbon fibres or mixtures with Dynel could be employed while glass fibers or cellulose fibers cannot be used.

The invention is further exemplified by illustrating certain variables regarding amounts of materials and conditions in Table II for practicing the invention in accordance with the teachings in the Examples.

Concerning the separators 22 employed in fabricating a battery, polyvinyl chloride and Dynel felt are examples of preferred materials. Polyethylene, cellulosives, rubber, and microporous glass could not be utilized. In the so called high rate electrode as exemplified As indicated in the Examples and Table II a ratio of bonding material to fibrous material is 4 to 1. However, this ratio can be extended to include a range of l to 4 for the bonding material and 0.25 to l for the fibres as fabrication. The electrode structure is not only selfsustaining but can be utilized with a metal grid or other suitable conductive backing thus making it available for use as a high rate lead dioxide electrode as well as based on a weight percentage. 5 a low rate one.

Hot pressing is utilized in the Examples for fabricat- Others may practice the invention in any of the nuing the electrode structure. However, this is only one merous ways which will be suggested by this disclosure means of mechanically fabricating. Heated rollers or a to one skilled in the art by employing one or more of heated substrate could be utilized in which case the mathe novel features disclosed or equivalents thereof. All terial composed of the lead dioxide, the bonding and suchpractice of the invention is considered to be a part fibrous materials is heated and simultaneously or subsehereof provided it falls within the scope of the apquently compacted. The heat may be supplied exterpended claims.

TABLEI Bonding conditions Voltage 50 Voltage I00 Voltage 850 Electrode Percent ma/in peak ma/in peak ma/in density Binder type by wt p.s.i. minimum (volts) minimum (volts) minimum g/cc (urhowax M... 7 7.000 1.74 4.95 (111116676X 20.M.. 10 7.000 L58 1.50 1.47 5.17 (616mm 6.000.. 7 7.000 1.76 1.69 1.67 5.48 4 7.000 1.78 1.71 1.68 4.89 5 7.000 1.76 1.68 1.67 4.84 5 7.000 a 0 1.65 1.52 1.42 4.84

QP-52.000 5 7,000 8L0 1.44 1 21 E0 5.10 3 7.000 1.70 1.64 1.49 5.95 3 7.000 1.71 1.66 1.58 5.86 4 7,000 1.70 1.63 1.51 5.72 3 7,000 1.53 1.40 1.00 6.01 4 7.000 1.58 1.32 50 5.78 3 7.000 1.23 0.80 0.79 5.98 5/5 7.000 1.60 1.45 E0 4.98 3.5/3.5 7.000 1.72 1.65 1.00 5.07

nally to the fixture used to form the electrode or it may TABLE ll be generated in s1tu v1a heat generated from fnctlonal BONDED LEAD DIOXIDE ELECTRODE RANGES forces (e.g. such as created by rolling powder between two rolers moving at different rates), ultrasonic energy, IAB RANGE MIN. MAX. OPT. UNITS impacting, microwave radiation, etc. Electrodes could FABRICATION also be prepared by exposing the powder, composed of Pressure 10,000* 20,000 16,000 Load the lead dioxide, the bonding and fibrous materials, to -gorganic fumes (such as methylethylketone) so as to p i Temp 90* 150* 120 C. make the plastic binder material tacky and then comz Particle pacting the treated powder. The solvent vapor could 40 gg' g 37 250 Mcmns subsequently be removed either by heating and/or Binder (Geon) 3 4 3 w/% Additives using reduced pressure. A further approach would be Nickel Powder 4 w/% to apply a slurry of PbO -Geon binder and methylethyl- Carbon ketone to a solid substrate (using a variety of thick filmgfi g: 4 1 TBS W mg techniques such as a doctor blade, sllk screen, etc.) 5 Dynel V4 1 1 Wm removing the methylethylketone and hot rolling the re- Uncoated P00 0. 15 ,w/%

Solka Floc 0 5 0 w/% sulttng stock to increase electrode density. I ELECTRODE DIMENSIONS As shown by the chart 1n FIG. III of the drawing, a Low Rate Electmde battery formed from the electrode structure composed Weight 2 3; of the bonding and fibrous materials with the lead diox- 50 Thickness 0500 e ec 1de particles operates over a period of 80 hours with a High Rate voltage ranging between 1.5 and 2.0 volts and at a tem- ,welght ng a: perature of 50 C. Performance ranges are shown in Thickness 0370 0578 (M84 mm Table III and FIGS. III, IV, V, and VI which indicates Electrolyte 1 15 ml P cell *absolute limit-above max. range or below min. range electrodes ,the long life, efficiency, and durability of the novel could not be made.

TABLE III PERFORMANCE HIGH RATE ELECTRODE RANGE MIN. MAX. 0 UNITS Current 0.1 300 20 ma/cm Temperature -60 I00 10 C. Activated Stand at RT 72 less Hours than 24 LOW RATE ELECTRODE Current 0.1 0.5 0.1 ma/cm Activated Stand at 50C. 10 79 -48 Hours We claim:

1. An electrochemical primary battery comprising: a metallic anode; fluoroboric acid as an electrolyte and a cathode composed of lead dioxide particles and a bonding material for said lead dioxide particles, said bonding material being compactly and homogeneously mixed to form an electrode structure, said lead dioxide being substantially uniformly mixed with said bonding material, said bonding material being compatible with said lead dioxide making the lead dioxide accessible to and consumable by said fluoroboric acid, while being at least partially inert to said fluoroboric acid.

2. The electrochemical battery as defined in claim I further including a synthetic fibrous material, said fibrous material being compactly and homogeneously mixed with said lead dioxide and said bonding material, said fibrous material being compatible with said lead dioxide making the lead dioxide accessible to and consumable by said fiuoroboric acid, while being at least partially inert to said fluoroboric acid.

3. The electrochemical battery as defined in claim 2 wherein said metallic anode comprises two metallic lead anodes with insulating separators between said anodes and said electrode structure.

4. The electrochemical battery as defined in claim 2 wherein said bonding material is a resin and the ratio of resinous material to fibrous material is in the range of l to 4 and 0.25 to l as based on a weight percentage.

5. The electrochemical battery as defined in claim 2 wherein said fibres are composed of a vinyl chlorideacrylonitrile copolymer resin.

6. The electrochemical battery as defined in claim 2 wherein said fibres are an equal mixture of carbon and a vinyl chloride-acrylonitrile copolymer resin.

7. The electrochemical battery as defined in claim 3 further including a metallic substrate for said cathode comprising a lead dioxide plated nickel.

8. The electrochemical battery as defined in claim 3 wherein said insulating separators are polyvinyl chloride or a vinyl chloride-acrylonitrile copolymer felt resin.

9. The electrochemical battery as defined in clain 2 wherein said bonding material is a vinyl chloride-vinyl acetate resin.

10. The electrochemical battery as defined in claim 2 wherein the ratio of said bonding material to said fibrous material is approximately 4 to 1 as based on a weight percentage.

11. The electrochemical battery as defined in claim 7 wherein said battery is composed of several cells of said anodes and cathodes and fluoroboric acid is present in an amount of approximately 1.5 milliliters per cell. 

2. The electrochemical battery as defined in claim 1 further including a synthetic fibrous material, said fibrous material being compactly and homogeneously mixed with said lead dioxide and said bonding material, said fibrous material being compatible with said lead dioxide making the lead dioxide accessible to and consumable by said fluoroboric acid, while being at least partially inert to said fluoroboric acid.
 3. The electrochemical battery as defined in claim 2 wherein said metallic anode comprises two metallic lead anodes with insulating separators between said anodes and said electrode structure.
 4. The electrochemical battery as defined in claim 2 wherein said bonding material is a resin and the ratio of resinous material to fibrous material is in the range of 1 to 4 and 0.25 to 1 as based on a weight percentage.
 5. The electrochemical battery as defined in claim 2 wherein said fibres are composed of a vinyl chloride-acrylonitrile copolymer resin.
 6. The electrochemical battery as defined in claim 2 wherein said fibres are an equal mixture of carbon and a vinyl chloride-acrylonitrile copolymer resin.
 7. The electrochemical battery as defined in claim 3 further including a metallic substrate for said cathode comprising a lead dioxide plated nickel.
 8. The electrochemical battery as defined in claim 3 wherein said insulating separators are polyvinyl chloride or a vinyl chloride-acrylonitrile copolymer felt resin.
 9. The electrochemical battery as defined in clain 2 wherein said bonding material is a vinyl chloride-vinyl acetate resin.
 10. The electrochemical battery as defined in claim 2 wherein the ratio of said bonding material to said fibrous material is approximately 4 to 1 as based on a weight percentage.
 11. The electrochemical battery as defined in claim 7 wherein said battery is composed of several cells of said anodes and cathodes and fluoroboric acid is present in an amount of approximately 1.5 milliliters per cell. 